Projection type display apparatus

ABSTRACT

In a projection type display apparatus for enabling to display an image, by projecting an image on an image display element(s), enlargedly, upon a nearly horizontal surface, such as, a table, a reflection mirror for reflecting a light from a light source is so disposed that an optical axis of the light source is nearly perpendicular to an optical axis of a lens group having a plural number of lens elements, which are disposed symmetric with respect to the optical axis.

CLAIM OF PRIORITY

This application is a continuation of application Ser. No. 12/023,151,filed on Jan. 31, 2008, currently pending, which claims the benefit ofJapanese Application No. JP 2007-046386, filed Feb. 27, 2007 in theJapanese Patent Office, the disclosures of which are incorporated hereinby reference.

BACKGROUND OF THE INVENTION

The present invention relates to a projection type display apparatus forenabling image display, by projecting an image on a image displayelement(s), enlargedly, upon a nearly vertical surface, and also forenabling image display upon a nearly horizontal surface, such as, adesk, etc.

As is described in Japanese Patent Laying-Open No. Hei 5-134213 (1993),there is already known a projection type image display apparatus forprojecting an image upon a screen, enlargedly, in an oblique directionthereto, while shifting the projection image or picture into thevertical direction with respect to an optical axis of the projectionoptic system, with using an additional optic system, which is inclinedto the optical axis of the projection optic system by a predeterminedangle. However, the additional optic system mentioned herein (i.e., anafocual converter) is an optic system having a function of convertingthe size of the projection image or picture, and it is for obtaining arectangular projection image with compensating/reducing distortions onthe projection screen, which are generated accompanying with theprojection from the direction oblique to the screen.

[Patent Document 1] Japanese Patent Laying-Open No. Hei 5-134213 (1993)

Within almost manners of using the conventional projection type displayapparatus, as is shown in FIG. 13, while providing a screen (not shownin the figure) on the nearly vertical surface, such as, a wall surface19, etc., the projection type display apparatus 101 is disposed on abase 20 or the like away from the wall surface 19, thereby projecting aprojection image or picture on said screen. Hereinafter, such conditionof providing the projection type display apparatus 101, as is shown inFIG. 13, is called “nearly horizontal disposition”.

In addition to the condition of use thereof as was motioned above, inrecent years is increasing a demand of projecting the image or pictureon the nearly horizontal surface, such as, a table or the like.

FIGS. 12( a) and 12(b) are views for showing the condition of projectingthe image upon the nearly horizontal surface, such as, the table 14,etc., with using the conventional projection type image displayapparatus 101. As is shown in FIG. 12( a), the conventional projectiontype image display apparatus 101 is fixed on a ceiling 15 by means of afixing member 16, so that the projection is directed downwardly, andthereby displaying the projection image 5 on the table 14. Thus, theprojection type image display apparatus 101 must be fixed on theceiling. However, it should not be limited only to the way or manner ofuse, i.e., projecting upon the nearly horizontal surface, such as, thetable, etc., for example, as is shown in FIG. 12( a). Of course, thereis also other way of use, i.e., projecting upon the nearly verticalsurface, such as, the wall surface, etc., as was shown in FIG. 13.Accordingly, there is generated a work of attaching/detaching of theprojection type display apparatus 101 onto/from the ceiling 15;therefore being inferior in the usability thereof.

Also, there is other way of projection the image upon the table 14 whilebending an optical path of projection; i.e., as is shown in FIG. 12( b),the projection type display apparatus 101 is disposed on the table 14,so as to project upward, while disposing a reflection mirror on the wayof the optical path of projection thereof (being fixed on the table 14by means of the fixing member 18). In case of this method, since thereis no necessity for the projection type display apparatus 101 to befixed, and also since it is on the table 14, it is possible to projectthe image upon the nearly vertical surface, such as, the wall surface,etc., as is shown in FIG. 13, easily, only by disposing the projectiontype display apparatus 101 with changing the projection directionthereof. Hereinafter, such condition of disposing the projection typedisplay apparatus, as shown in FIGS. 12( a) and 12(b), is called “nearlyvertical disposition”.

BRIEF SUMMARY OF THE INVENTION

However, within the projection optic unit described in the JapanesePatent Laying-Open No. Hei 5-134213 (1993), because of eccentricity ordecentering of the additional optic system (i.e., the afocualconverter), which is disposed on the projection surface side, it isdifficult to achieve widening the angle of field thereof. For thisreason, the distance from the projection apparatus up to the projectionsurface (hereinafter, being called “projection distance”) comes to belong, in order to obtain the projection image having a necessarymagnification. Thus, in case where projection is conducted as shown inFIG. 12( b) with using the projection optic unit described in theJapanese Patent Laying-Open No. Hei 5-134213 (1993), it is necessary tolocate the reflection mirror 17 in the above, so as to obtain theprojection image having the necessary magnification. Further, thereflection mirror 17 is needed only in the case when projecting upon thenearly horizontal surface, such as, the table 14, etc., and it may beprovided/removed from, depending upon the condition of use thereof;therefore not preferable or superior in the usability thereof. Even ifpossible to achieve the widening the angle of field, but since thereflection mirror 17 projects, largely, onto the side of the projectionimage 5 (i.e., into the left-hand side direction in the figure), in theconfiguration thereof, there is also caused a drawback that, for aperson at the opposite of the projection image 5 of the projection typedisplay apparatus 101, it is impossible to see the projection image 5due to obstruction of this reflection mirror 17.

According to the present invention, being accomplished by taking thedrawbacks mentioned above into the consideration thereof, an objectthereof is to provide a projection type display apparatus for enablingto display an image or picture, through projecting the image or pictureon an image display element, enlargedly, upon the nearly horizontalsurface, such as, the table, etc.

According to one aspect of the present invention, a reflection mirrorfor reflecting a light from a light source is so disposed that anoptical axis of the light source is nearly perpendicular to an opticalaxis of a lens group having a plural number of lens elements, which aredisposed symmetric with respect to the optical axis.

According to the present invention, it is possible to project the imageor picture, with suppressing distortions and/or aberrations thereof,while bringing the distance up to the projection surface (i.e., thescreen) to the minimum through widening the angle of field, andtherefore achieving a projection type display apparatus, beingpreferable in the performances or capability thereof and further beingconvenient and superior in the usability thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

Those and other objects, features and advantages of the presentinvention will become more readily apparent from the following detaileddescription when taken in conjunction with the accompanying drawingswherein:

FIG. 1 is a perspective view for showing the entire of a projection typedisplay apparatus, according to an embodiment 1 of the presentinvention;

FIG. 2 is a cress-section view of a projection optic unit of theprojection-type image display apparatus, according to an embodiment 1;

FIG. 3 is a perspective view for showing the entire of the projectiontype display apparatus, according to an embodiment 1, under thecondition of projecting an image upon the nearly vertical surface;

FIG. 4 is a perspective view for showing an example of disposition ofthe lenses within the projection optic unit shown in FIG. 2;

FIGS. 5( a) and 5(b) are cross-section views for explaining lenssurfaces of the projection optic unit mentioned above;

FIG. 6 is a cross-section view for explaining an optical axis of theprojection optic unit;

FIG. 7 is a perspective view for showing the entire of the projectiontype display apparatus, but differing from that shown in FIG. 1according to the embodiment 1;

FIG. 8 is a perspective view for showing an example of the lensdisposition of the projection optic unit within the projection typedisplay apparatus shown in FIG. 7;

FIG. 9 is a perspective view for showing the entire of the projectiontype display apparatus shown in FIG. 7, under the condition ofprojecting an image upon the nearly vertical surface;

FIG. 10 is a YZ cross-section view for showing optical paths within theprojection type display apparatus according to the embodiment 1;

FIG. 11 is an XZ cross-section view for showing optical paths within theprojection type display apparatus according to the embodiment 1;

FIGS. 12( a) and 12(b) are views for showing the conventional projectiontype display apparatus, under the condition of projecting an image uponthe nearly horizontal surface; and

FIG. 13 is a view for showing the conventional projection type displayapparatus, under the condition of projecting an image upon the nearlyvertical surface.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Hereinafter, embodiments according to the present invention will befully explained by referring to the attached drawings.

FIG. 1 attached herewith is a perspective view for showing a projectiontype display apparatus according to an embodiment 1. In this figure, theprojection type display apparatus 100 has a housing having a box-likeshape, within which it comprises an image display element 1 fordisplaying an image or a picture inputted from an outside thereof, and alight source 8, such as, a lamp for generating a white light of highbrightness, or the like, for example, and wherein the light emitted fromthe light source 8 changes the direction thereof by around 90 degreeupon a reflection mirror (i.e., a first reflection portion), to beirradiated upon the image display element 1. And, it also mounts aprojection optic unit for irradiating an optical image, enlargedly,which is modulated on the image display element 1. The projection opticunit is constructed with a transmission (lens) optic system, which isbuilt up with two (2) lens groups, including a prism (not shown in thefigure), a first (or front) lens group 2, and a second (or rear) lensgroup 3, and a reflection optic system including a reflection mirrorhaving a reflection surface of freely-curved surface configuration(hereinafter, being called “freely-curved surface mirror) 4, being notrotationally symmetric (i.e., being rotationally asymmetric). The lightreflection upon the freely-curved surface mirror 4 (i.e., the secondreflection portion) builds up an optical image on a table 14, and isdisplayed as a projection image or picture 5. Thus, the projection imageid displayed on the surface, being same to the surface, on which theprojection type display apparatus 100 is mounted (i.e., an upper surfaceof the table 14).

FIG. 2 is a view for showing the projection optic unit of the projectiontype display apparatus, according to the embodiment 1. However, thisFIG. 2 shows a cross-section view (i.e., a YZ cross-section) when seeingthe apparatus in the X direction in FIG. 1. As was mentioned above, theprojection optic unit has the image display element 1 for emitting adesired image or picture upon incidence of the light from the lightsource 8, a prism 10, the transmission (lens) optic system, being builtup with two (2) sets of lens groups including the first lens group 2 (orfront lens group) and the second lens group 3, and further thereflection optic system including the freely-curved mirror 4.

As the image display element 1 is shown an example of adopting thetransmission type, such as, the liquid crystal panel, representatively,for example, however an image display element of a reflection type maybe applied in the place thereof. Also, as the image display element 1may be applied a one that of a method, i.e., composing or synthesizing aplural number of images or pictures, R, G and B, such as, a three-platestype, and in that case, it is necessary to provide a prism, or the like,for use of composing the images.

Within the projection optic unit explained in the above, the light fromthe image display element 1 through the prism 10 is firstly incidentupon the first lens group 2, i.e., being the lens optic system. Althoughwill be explained later, this first lens group 2 includes a pluralnumber of refraction lenses having a rotationally symmetric surfaceconfiguration and having a positive power and a negative power.Thereafter, the light emitting from this first lens group 2 passesthrough the second lens group 3, which is made up with a plural numberof lenses, including a plural number (two (2) pieces in theembodiment 1) of lenses having the freely-curved configuration, notrotationally symmetric (i.e., rotationally asymmetric), on at least oneof the surfaces thereof. And, the light emitting from this second lensgroup 3, further after being reflected, enlargedly, upon the reflectionoptic system including the free-curved surface mirror 4, is projectedupon the table 14 (not shown in the figure), as a predeterminedprojection image or picture 5.

However, in the embodiment 1, as is apparent from FIG. 2, i.e.,differing from the optic system of shifting the projection screen (i.e.,the display element) to the optical axis of the projection system, andfurther disposing the additional optic system inclining by thepredetermined angle with respect to the optical axis of the objectionsystem, as was in the background arts mentioned above, the image displayelement 1 is so disposed that a center of the display screen thereof islocated around the optical axis of the lens optic system (i.e., forminga co-axial optic system). Accordingly, the light beam 11, emitting fromthe center of the display screen of the image display element 1, passingthrough an incident pupil of the lens optic system, and directing towarda center of the screen on the projection image, advances almost alongthe optical axis of the lens optic system (including the first lensgroup 2 and the second lens group 3). Hereinafter, this will be called“screen center light beam”. Thereafter, this screen center light beam11, after being reflected at a point P2 upon the reflection surface ofthe freely-curved surface mirror 4, is incident at a point P5 at thescreen center upon the projection image 5, obliquely from −Y direction(i.e., the left-hand side direction) with respect to a normal line 7 onthe projection surface. This angle will be mentioned “an obliqueincident angle”, and is expressed by “θs”, hereinafter. This indicatesthat the light beam passing through along the optical axis of the lensoptic system is incident upon the projection surface, obliquely, andmeans that the optical axis of the lens optic system is inclined,substantially, with respect to the projection surface (i.e., forming anoblique incident system).

However, as was mentioned above, when entering the light beam,obliquely, onto the projection surface, then the configuration of theimage projected from the image display element 1 comes from arectangular into a trapezoidal one; i.e., generating various kinds ofaberrations, including a zooidal distortion, and others than that, dueto the fact of not being rotationally symmetric with respect to theoptical axis. However, in the embodiment 1, those are compensated bymeans of the second lens group 3 of the lens optic system. And, with thefreely-curves surface mirror, i.e., the reflection optic system, therecan be obtained an advantage of generating no magnification coloraberration due to widening the angle of field.

In particular, reflecting the light beam emitting from the image displayelement 1 upon the reflection surface of the freely-curved surfacemirror 4, to be incident upon the projection image 5, obliquely, it ispossible to obtain an amount of eccentricity (i.e., an eccentric angle),being large comparing to that of the light, which can be obtainedthrough the lenses, and also, since the aberration hardly occurs,therefore it is possible to suppress the apparatus from large-sizingthereof, and further to obtain the widening of the angel of field. Thus,it is possible to obtain an optic system, being small in the diameterthereof, comparing to that of suppressing the trapezoidal distortion bydecentering the additional optic system (i.e., the afocual converter),of the background art mentioned above, in particular, the lens systemincluding the first lens group 2 and the second lens group 3.

Also, since the light incident upon the reflection surface of thereflection mirror 4, which builds up the reflection optic system, isenlarged up to a predetermined size, to be projected, by means of thelens optic system, as was mention above, and therefore it can bemanufactured, easily. Thus, the lens optic system can be manufacturedseparate from the reflection optic system, and thereafter both of themcan be fixed within the housing of the apparatus, adjusting thepositions thereof, and this is suitable for mass production thereof, inparticular.

Also, disposing the second lens group 3 for compensating the trapezoidaldistortion, etc., in a front of the first lens group enable to reducethe distance between the second lens group and the first lens group 2 inthe disposition thereof, and therefore it is possible to make theapparatus compact, as a whole thereof, mounting the projection opticunit therein.

In this manner, bombing the lens optic system of the transmission typehaving the freely-curves surface configuration and the reflection opticsystem having the freely-curved surface configuration enables to achievethe widening the angle of field, which is strongly demanded, withcertainty and relative easiness, and further to achieve the projectiontype display apparatus for bringing the apparatus as the whole to becompact.

FIG. 3 shows the projection type display apparatus 100, according to theembodiment 1, in the near horizontal disposition thereof, under thecondition of displaying the projection image 5 on the near verticalsurface, such as, the wall surface 19, etc. In this manner, onlychanging the method for disposing the projection type display apparatus100 enables to display the projection image on both of the surfaces,i.e., on the near horizontal surface, such as, the table or the like, oron the nearly vertical surface, such as, the wall surface or the like,for example.

When projecting upon the nearly horizontal surface, as is shown in FIG.1, in many cases, viewing is made from the left-hand side direction inthe figure (i.e., +Y direction). Accordingly, below the projectionscreen 5 is in +Y direction, as is shown by an image of a person 150. Onthe other hand, when projecting upon the near vertical surface, as isshown in FIG. 3, below the projection screen is in the lower directionin the figure (i.e., −Y direction). In this manner, since the up/downdirection of the picture projected differs depending upon the projectionsurface, there is a possibility the picture is upside-down in onecondition, if being as it is. In this case, there is necessity ofdisplaying the picture reversing up/down and left/right, on the imagedisplay element 1. The reversal of those pictures (i.e., optical images)may be made depending upon the condition of use by a user through areversing portion (not shown in the figure), or may be provide a gravitysensor or the like, within the apparatus, for detecting the condition ofdisposing the apparatus by a detection portion (not shown in thefigure), and thereby exchanging it automatically. In the descriptionmentioned above, although the reversal is made on both up/down andleft/right, but may be made only on up/down.

In this instance, disposing the reflection mirror 9 between the lightsource 8 and the image display element 1 brings an optical axis 8 c ofthe light source 8 to be perpendicular to an optical axis 3 c of thesecond lens group 3. As the light source 8 may be applied, in general, amercury lamp of high pressure, a halogen lamp, a xenon lamp, LED, alaser light source, etc., in many cases. For example, when using themercury lamp of high pressure, the lamp is designed to have a longlifetime, if being used while turning the direction of the optical axisof the light source 8 into either one of the horizontal direction or thevertical direction to that of the gravity. Thus, there is a problem thatthe lifetime comes to be short when the lamp is used in the directionsother than the directions that are designed to obtain the long lifetime.In the projection type display apparatus 101, according to theembodiment 1, directing the optical axis 8 c of the light source 8perpendicular to the optical axis 3 c of the second lens group 3 enablesthe optical axis 8 c of the light source 8 to be nearly horizontal evenin either condition, i.e., the nearly vertical disposition (see FIG. 1)or the nearly horizontal disposition (see FIG. 3), and thereby achievingthe long lifetime thereof.

FIG. 4 and FIGS. 5( a) and 5(b) show the lens surfaces of opticalelements within the projection optic unit, including the reflectionoptic system therein. Herein, the coordinate axis X is same to X inFIGS. 1 and 2, while assuming that the optical axis of the first lensgroup 2 and the second lens group 3 is Z′-axis and the axisperpendicular to X and Z′ is Y′-axis. Though will be mentioned later,the Z′-axis is different from the Z-axis shown in FIGS. 1 and 2. FIG. 5(a) shows a Y′Z′ cross-section and FIG. 5( b) a XZ′ cross-section in FIG.4, respectively.

As is shown in those figures, within the lens optic system, an imageemitted from the image display element 1 through the prism 10 is firstlyincident upon the first lens group 2, including a plural number oflenses therein, which has the rotationally symmetric configuration. Aswas mentioned above, the first lens group 2 includes a spherical lens,being rotationally symmetric, and also an aspheric lens therein.

Also, the second lens group 3 is constructed with at least two (2)pieces of free curved or sculptured surface lenses. As is shown in thosefigures, a freely-curved surface lens 31 nearest to the reflectionsurface S23 of the reflection mirror 4, directs a concave thereof intothe direction of light emission, and a curvature of a portion, where thelight passes through to be incident upon −Y′ side end of the projectionsurface (a lower side in FIG. 4), is determined to be larger than thatof a portion, where the light passes through to be incident upon +Y′side end of the projection surface (an upper side in FIG. 4). Thus, itis assumed that, the freely curved surface lens has such theconfiguration, i.e., being curved directing the concave into thedirection of emission of that light, and having the curvature in theportion where the light passes through to be incident upon the −Y′ sideend of the projection surface, being larger than that in a portion wherethe light passes through to be incident upon +Y′ side end of theprojection surface.

Also, according to the embodiment 1, they are constructed to fulfill thefollowing condition. Thus, within the cross-section shown in FIG. 2mentioned above, it is assumed that the light incident upon a point P6at an upper end of picture on the screen 5, being emitted from a lowerend of screen on the image display element 1 and passing through acenter of the entrance pupil of the first lens group 2, is a light 12.It is assumed that an optical path length is “L1” for this light 12 toreach the point P6 from a point P3 where this light 12 passes throughthe free curved surface mirror 4. Also, it is assumed that the lightincident upon a point P4 at the lower end of picture on the screen 5 isa light 13, being emitted from the upper end of screen of the imagedisplay element 1 and passing through the center of the entrance pupilof the first lens group 2. It is assumed that the optical pass length is“L2” for this light 13 to reach the point P4 from the point P1 wherethis light 13 passes through the free curved surface mirror 4. And, theprojection optic unit mentioned above is so constructed that the “L1”and the “L2” satisfy the following equation (Eq. 1):

|L1−L2|<1.2*sin θs*Dv

However, where “Dv” is a size of the picture on the screen, within thecross-section shown in FIG. 2, and in other words, it is a distance fromthe point P6 at the upper end of picture to the point P4 at the lowerend thereof on the screen. Also, “θs” is the oblique incident anglementioned above.

On the other hand, although the image display element 1 mentioned aboveis disposed in such a manner that the center of the display screenthereof is located on the optical axis of the lens optic systemmentioned above, or alternatively, it is preferable to dispose it insuch a manner that the normal line on the said display screen isinclined a little bit to the optical axis of the lens optic systemmentioned above, as is shown in FIG. 6 attached herewith.

Further, judging from seeing FIG. 2, as was mentioned previously, theoptical path length reaching from the point P3 to the point P6 is longerthan the optical path length reaching from the point P1 to the point P4.This means that the image point P6 is farther from than the image pointP4. Then, if an object point (i.e., a point in the display screen)corresponding to the image point P6 on the screen is located at a pointnearer to the lens optic system and also if an object pointcorresponding to the image point P4 is located at a position fartherfrom the lens optic system, it is possible to compensate the inclinationof an image surface. For that purpose, as will be shown in FIG. 6, it ispreferable to incline a normal line vector at a center on the displayscreen of the image display element 1, a little bit, with respect to theoptical axis of the lens optic system, within a plane defined to includethe normal line of the screen 5 and the light at the center of thescreen therein. And, it is preferable that the direction of thatinclination is opposite to the direction into which the projection imageor screen 5 is positioned.

Further, the method for inclining an abject surface is already known forthe purpose of obtaining an image surface inclined to the optical axis,however within a practical region of the angle of view, deformationsasymmetric to the optical axis are produced upon the image surface,which is obtained through the inclination of the object surface, andtherefore it is difficult to make compensation by means of a projectionlens, which is rotationally symmetric. According to the embodiment 1,because of applying the free curved surface lens 31 and further also thefree curved surface lens 32, which are rotationally asymmetric, withinthe second lens group 3 mentioned above, it is possible to treat withthe deformations upon the asymmetric image surface. For this reason,inclination of the object surface, i.e., the display surface of theimage display element, enables to reduce the distortions of lowdimensions on the image surface, greatly, and therefore it is effectivefor assisting the compensation of aberrations due to the free curvedsurface.

Next, with the function of each of the optical elements mentioned above,in particular, within the lens optic system mentioned above, the firstlens group 2 (i.e., lenses 21 to 25), they build up a main lens forprojecting the display screen of the image display element 1 onto theprojection image (or screen) 5, and also compensate the basicaberrations within the optic system that is rotationally symmetric. And,the second lens group 3 (i.e., lenses 31 to 34) within the lens opticsystem mentioned above, they are made up with lenses, each having thefree curved surface, being not rotationally symmetric (i.e.,rotationally asymmetric). Further, since the reflection optic system 4mentioned above is built up with the reflection surfaces, each havingthe free curved surface configuration that is not rotationallysymmetric, then it mainly compensates the aberration, which is produceddue to the oblique incidence of the light. Thus, within such thestructures as was mentioned above, the mirror 4 building up thereflection optic system mentioned above mainly compensates thetrapezoidal distortion, while the second lens group 3 of the lens opticsystem mainly compensate the asymmetric aberrations, such as, thedistortion on the image surface, etc.

As was mentioned above, according to the present embodiment, thereflection optic system mentioned above is built up with one (1) pieceof the reflection surface (i.e., mirror) 4 having the free curvedsurface configuration that is not rotationally symmetric, while thesecond lens group 3 of the lens optic system mentioned above includestwo (2) pieces of the transmission-type lenses (i.e., the lenses 31 and32 on the side of reflection mirror 4), in the structures thereof.Herein, the free curved surface mirror 4 is curved directing a convexinto the direction of reflection. And, a curvature on a portion of thefree curved surface mirror 4, reflecting the light to be incident upon alower end of the screen, is determined to be larger than the curvatureof a portion thereof, reflecting the light to be incident upon an upperend of the screen. Or, a portion reflecting the light to be incidentupon the lower end of the screen may be defined into a configurationconvex to the reflecting direction of the light, on the other hand, aportion reflecting the light to be incident upon the upper end of thescreen into a configuration concave to the reflecting direction thereof.

The distance between an origin of coordinates on the reflection surface(i.e., the mirror) 4 of the reflection optic system and the lens surfacenearest to the reflection surface (i.e., the mirror) 4 among the firstlens group 2, in the direction of the optical axis, it is preferable tobe set as five (5) times large as the focus distance of the first lensgroup 2 or more than that. With this, it is possible to compensate thetrapezoidal distortion by the reflection surface of the reflection opticsystem, having the free curved surface configuration, more effectively,and thereby obtaining a preferable performance.

FIGS. 7, 8 and 9 are views for explaining the projection type displayapparatus, in particular, in the case where the reflection mirror 35 isdisposed between the first lens group 2 and the second lens group 3.

As shown in those figures, by the function of a reflection (returning)mirror 35 (i.e., the first reflection portion), the optical axis of thefirst lens group 2 is bent by about 90 degree to the optical axis of thesecond lens group 3. In this instance, if not disposing the reflectionmirror between the image display element 1 and the light source 8, theangle defined between the optical axis 8 c of the light source 8 and theoptical axis 3 c of the second lens group 3 becomes nearly vertical. Thefunction and the effect thereof are similar to that mentioned above,therefore the explanation thereof will be omitted herein.

Next, explanation will be made on the numerical values of theembodiment, according to the embodiment 1.

Firstly, explanation will be made on the details of the projection opticunit, according to the present embodiment explained in the above, byreferring to FIGS. 10 and 11 attached herewith and further tables 1 to 4below, while showing the detailed numerical values of the opticalelements, including the lens optic system and the reflection opticsystem therein. However, FIGS. 8 and 9 attached herewith are diagramsfor showing light beams in the optic system according to the presentinvention, upon basis of an example of first numerical values. Thus,within XYZ rectangular coordinates system shown in FIG. 1 mentionedabove, FIG. 10 shows the Y-Z cross-section, and FIG. 11 shows X-Zcross-section. Further, this FIG. 11 shows an example of disposing abending mirror 35 on the way between the first lens group 2 and thesecond lens group 3 building up the lens optic system, as is shown inthe details thereof in FIGS. 5 and 6, and thereby bending the light pathinto the X-axis direction, once.

The light emitted from the image display element 1 shown at theleft-hand side in FIG. 10, firstly passes through the first lens group 2built up with only lenses, each having only surfaces that arerotationally symmetric, among the lens optic system including the pluralnumber of lenses therein. Then, it passes through the second lens group3 including the free curved surface lens that is rotationallyasymmetric, and is reflected upon the reflection surface of the freecurved surface mirror 4 within the reflection optic system. Thereafter,the reflecting light thereupon is incident upon the screen 5.

Herein, the first lens group 2 of the lens optic system is built up withthe plural number of lenses, all of which have a refracting interface ofrotationally symmetric configuration, and four (4) of the refractinginterfaces of those lenses have aspheric surfaces, each beingrotationally symmetric, and others have the spherical surfaces. Theaspheric surface being rotationally symmetric, which is used therein,can be expressed by the following equation (Eq. 2), with using a localcylindrical coordinates system for each

$Z = {\frac{{cr}^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)c^{2}r^{2}}}} + {A \cdot r^{4}} + {B \cdot r^{6}} + {C \cdot r^{8}} + {D \cdot r^{10}} + {E \cdot r^{12}} + {F \cdot r^{14}} + {G \cdot r^{16}} + {H \cdot r^{18}} + {J \cdot r^{20}}}$

surface:

Where, “r” is the distance from an optic axis, and “Z” represents anamount of sag. Also, “c” is the curvature at an apex, “k” a conicalconstant, “A” to “J” coefficients of a term of power of “r”.

On the other hand, the free curved surfaces of the second lens group 3,being the lens optic system mentioned above, can be expressed by thefollowing equation (Eq. 3), including polynomials of X and Y, withapplying the local coordinates system (x, y, z) assuming the apex oneach surface to be the origin.

$Z = {\frac{{cr}^{2}}{1 + \sqrt{1 - {\left( {1 + k} \right)c^{2}r^{2}}}} + {\sum\limits_{m}{\sum\limits_{n}\left( {{C\left( {m,n} \right)} \cdot x^{m} \cdot y^{n}} \right)}}}$

Where, “Z” represents an amount of sag of the free curved surfaceconfiguration, in particular, into the direction perpendicular to X- andY-axes, “c” the curvature at the apex, “r” the distance from the originwithin a plane of X- and Y-axes, “k” the conical constant, and C(m,n)the coefficients of the polynomials.

Next, the following table 1 shows the numerical data of the opticsystem, according to the embodiment 1. In this table 1, S0 to S23correspond to the marks S0 to S23 shown in FIG. 5 mentioned above,respectively. Herein, the mark S0 shows the display surface of the imagedisplay element 11, i.e., the object surface, and S23 the reflectionsurface of the freely curved surface mirror 5. Also, though not shown inthose figures, but a mark S24 shows an incident surface of theprojection image or screen 5 shown in FIG. 2 mentioned above, i.e., theimage surface.

TABLE 1 Surface Rd TH nd νd S0 Infinity 10.00 S1 Infinity 31.34 1.5182748.0 S2 Infinity 7.06 S3 246.358 4.65 1.85306 17.2 S4 −84.858 18.00 S5*−83.708 9.00 1.49245 42.9 S6* −75.314 0.10 S7 41.651 9.32 1.49811 60.9S8 −42.282 2.50 1.76014 20.0 S9 29.550 0.10 S10 29.476 9.00 1.49811 60.9S11 −79.153 25.90 S12 Infinity 9.10 S13 −265.353 6.00 1.85306 17.2 S14−53.869 65.00 S15 −24.898 4.19 1.74702 33.2 S16 −58.225 9.00 S17*−27.332 10.00 1.49245 42.9 S18* −32.424 2.50 S19# Infinity 8.00 1.4924542.9 S20# Infinity 20.51 S21# Infinity 8.00 1.49245 42.9 S22# Infinity160.99 S23# Infinity −705.00 REFL

Also, in the table 1 mentioned above, “Rd” is the radius of curvaturefor each surface, and it is presented by a positive value in case whenhaving a center of curvature on the left-hand side of the surface inFIG. 3 mentioned above, while by a negative value in case when having iton the right-hand side, contrary to the above. Also, “TH” is thedistance between the surfaces, i.e., presenting the distance from theapex of the lens surface to the apex of the next lens surface. Thedistance between the surfaces is presented by a positive value in casewhen the next lens surface is at the left-hand side, while by a negativevalue in case when it is at the right-hand side, with respect to thatlens surface.

Further, in the table 1 mentioned above, S5, S6, S17 and S18 areaspheric surfaces, being rotationally symmetric, and also in this table1, they are attached with “*” beside the surface numbers for easyunderstanding thereof, wherein coefficients of the aspheric surface ofthose four (4) surfaces are shown in the table 2 below.

TABLE 2 Surface Aspheric Surface Coefficients S5 K −11.7678542 C −1.159E−11 F 2.298642E−20  J −1.255E−26 A −2.7881E−06 D −3.2834E−14 G1.05201E−21 B 9.67791E−09 E 1.09359E−16 H 1.96001E−24 S6 K −5.4064901 C 2.0324E−12 F  3.0211E−19 J −1.4982E−26 A 6.14967E−07 D −2.2078E−14 G4.30049E−22 B 4.60362E−09 E −8.0538E−17 H 4.79618E−24 S17 K 1.106429122C −9.0262E−11 F −1.0521E−18 J −6.0837E−26 A −1.1068E−05 D −1.3984E−13 G−8.1239E−23 B 7.21301E−08 E  3.1153E−16 H 3.86174E−23 S18 K 0.742867686C −2.2719E−11 F 1.09398E−19 J 9.02232E−29 A 1.51788E−07 D −4.6853E−14 G1.62146E−22 B 2.10472E−08 E  2.9666E−17 H −3.0801E−25

Also, S19 to S22 in the table 1 mentioned above are the refractionsurfaces, each having the free curved surface configuration, whichbuilds up the second lens group of the lens optic system mentionedabove, and S23 is the reflection surface having the free curved surfaceconfiguration S23 of the reflection optic system, wherein they are shownby attaching “#” beside the surface numbers thereof. Values of thecoefficients for presenting the configurations of those five (5) freecurved surfaces are shown in the table 3 below.

TABLE 3 Surface Aspheric Surface Coefficients S19 C17 5.38933E−07 C34−1.2381E−09 C51 −7.4126E−14 K 0 C19 8.33432E−07 C36 1.13944E−09 C532.05074E−12 C4 0.013500584 C21 −4.6367E−08 C37 3.87771E−12 C55−9.2166E−13 C6 0.003493312 C22 −6.2643E−09 C39 1.04779E−11 C56−2.5867E−15 C8 −0.00083921 C24 −2.2449E−08 C41 1.80038E−11 C58−8.7122E−15 C10 −0.00032098 C26 −5.6706E−08 C43 5.23019E−11 C602.85321E−14 C11 8.59459E−06 C28 9.69952E−10 C45 1.69253E−11 C62−8.5084E−14 C13 2.14814E−06 C30 −1.1968E−10 C47   −2.7E−14 C641.25198E−13 C15 7.54355E−06 C32 −1.3638E−09 C49 7.30978E−13 C66−5.6277E−14 S20 C17 7.49262E−07 C34 −5.7462E−10 C51 −3.6141E−13 K 0 C191.19039E−06 C36 1.27396E−09 C53 8.54188E−14 C4 0.015488689 C21−1.2953E−07 C37 −4.7746E−12 C55 −5.3469E−13 C6 0.006553414 C22   5.115E−10 C39 7.32855E−12 C56 8.92545E−17 C8 −0.00116756 C24−2.1936E−08 C41 5.30157E−11 C58 −5.3434E−15 C10 −0.00033579 C26−5.9543E−08 C43 5.05014E−11 C60 1.96533E−14 C11  7.5015E−06 C282.03972E−08 C45 −2.1894E−11 C62 −1.3923E−13 C13 −2.5728E−06 C301.16701E−11 C47 −1.2515E−13 C64 1.06322E−13 C15 −1.3543E−06 C32−1.6198E−09 C49 7.64489E−13 C66 −4.6602E−15 S21 C17 −1.0379E−07 C342.81743E−10 C51 −8.1775E−15 K 0 C19  3.0082E−08 C36 6.05663E−10 C533.06022E−14 C4 0.015096874 C21 7.95521E−08 C37 8.39381E−13 C55−9.1775E−13 C6 0.009982808 C22 −1.3911E−09 C39 1.98531E−12 C56−7.8543E−17 C8 0.000358347 C24 9.33292E−10 C41 1.37477E−11 C58−8.9588E−16 C10 0.000209267 C26 3.54468E−09 C43 −1.0671E−11 C60−6.0768E−15 C11 −3.8593E−07 C28  4.1615E−09 C45 9.04109E−12 C62−1.9528E−14 C13 −6.8336E−06 C30 −1.2331E−11 C47 2.48401E−14 C64 2.6781E−14 C15 −2.2455E−05 C32 −2.3367E−10 C49 6.92603E−14 C66−1.4324E−14 S22 C17 −3.6973E−07 C34  4.8045E−10 C51 −2.9795E−13 K 0 C19−3.0682E−07 C36 1.43328E−10 C53 −2.5306E−14 C4 0.022813527 C214.12093E−08 C37 −2.0707E−12 C55 −3.9401E−13 C6 0.012060543 C224.07969E−09 C39 −4.9221E−12 C56 6.88651E−16 C8 0.000638931 C24 8.5986E−09 C41 −2.3681E−12 C58 1.55006E−15 C10 0.000196027 C26 2.1713E−08 C43 −2.1567E−11 C60 −1.4674E−15 C11 −7.1204E−06 C281.63499E−08 C45 −2.3679E−12 C62 −9.9822E−15 C13  −1.269E−05 C301.38704E−10 C47 −5.7167E−15 C64 2.72925E−14 C15 −2.5184E−05 C322.02372E−10 C49 −9.0337E−14 C66 −1.1966E−14 S23 C17 −1.1083E−09 C34−4.9118E−14 C51 −5.4918E−19 K 0 C19 −5.7768E−10 C36 8.12546E−14 C53−2.2569E−18 C4 0.001597194 C21 1.60076E−10 C37  −7.486E−17 C55−3.5657E−18 C6 0.001324181 C22 1.91534E−12 C39 6.80626E−16 C561.09883E−21 C8 1.37885E−05 C24 −1.0665E−11 C41 −5.1295E−17 C58−2.1535E−20 C10 1.34349E−05 C26 −8.6063E−12 C43 −3.6526E−16 C602.01763E−20 C11 −4.8064E−08 C28 −1.1125E−12 C45 1.46399E−15 C62−1.2016E−20 C13 5.24071E−08 C30 6.24714E−14 C47 −2.1563E−18 C643.21408E−21 C15 9.53861E−08 C32 −3.4381E−14 C49 2.86073E−18 C66−1.4922E−19

Also, according to the present invention, as is shown in FIG. 6, theobject surface, i.e., the display screen of the image display element 1is inclined by −1.163 degrees to the optical axis of the lens opticsystem mentioned above. However, with the direction of inclination, itis assumed that a positive value presents the direction, in which thenormal line on the object surface rotates into the clockwise directionwithin the cross-section shown this FIG. 6. Accordingly, according tothe present embodiment, it means that, within the cross-section shown inFIG. 6, the object surface is inclined into the anti-clockwise directionby 1.163 degrees from the position perpendicular to the optical axis ofthe lens optic system mentioned above.

Also, the free curved surface mirror 4 shown by the mark S23 in FIG. 5or 6 mentioned above is so disposed that, the normal line at the originof the local coordinates thereof, i.e., the Z-axis is inclined by around+29 degree from the position in parallel with the optical axis of thelens optic system mentioned above while positioning that origin of thelocal coordinates on the optical axis of the lens optic system mentionedabove. However, the direction of this inclination is assumed to bepositive in the anti-clockwise rotating direction, within thecross-sections shown in FIG. 5 or 6, similar to that of the objectsurface mentioned above, and therefore, it is inclined into theanti-clockwise rotation. With this, the light at the center of thescreen, emitting from the center on the screen of the image displayelement 1 and propagating almost along the optical axis of the lensoptic system mentioned above, after reflection upon S23, it propagatesinto a direction inclined by 58 degrees, i.e., 2 times large as theinclination angle with respect to the optical axis of the lens opticsystem mentioned above (see an arrow in the figure).

Further, in the present numerical embodiment, the conditions of theinclination and an offset of the local coordinates are shown in thetable 4 below, on each of the surfaces. In this table 4, values of theinclination angle and the offset are shown on the columns on theright-hand sides of the surface number, wherein “ADE” is a magnitude ofthe inclination within the surface in parallel with the cross-section ofFIG. 5, and a rule of display thereof is as mentioned above. Also, “YDE”is a magnitude of the offset, and the offset is set up into thedirection perpendicular to the optical axis within the surface inparallel with the cross-section of FIG. 5, and the offset below on thecross-section of FIG. 5 is assumed to be positive. However, also in theembodiments that will be explained hereinafter, the inclination and theoffset of an optical element are setup to be the direction within thecross-section in parallel with the cross-section shown therein.

TABLE 4 Surface ADE (°) YDE (mm) S0 −1.163 0.0 S23 29.000 0.0

However, as be seen from the tables 1 and 3 mentioned above, accordingto the present embodiment, it is apparent that the curvature “c” and theconic coefficients “k” are “0”. Thus, the trapezoidal distortion, beinggenerated due to the oblique incidence, is extremely large in thedirection of the oblique incidence, but the amount thereof is small inthe direction perpendicular to this. Accordingly, between the directionof the oblique incidence and the direction perpendicular to this, theremust be provided functions greatly different from each other, and it ispossible to compensate or correct the asymmetric aberration, preferably,without using the curvature “c” nor the conic coefficient “k”, beingrotationally symmetric and functioning in all directions.

Also, in the table 4 mentioned above, “ADE” of the surface S23 is sameto “θm” shown in FIG. 2, and “ADE” on the surface of the projectionimage or screen 5 is “θs”, as is shown in FIG. 2.

While we have shown and described several embodiments in accordance withour invention, it should be understood that disclosed embodiments aresusceptible of changes and modifications without departing from thescope of the invention. Therefore, we do not intend to be bound by thedetails shown and described herein but intend to cover all such changesand modifications that fall within the ambit of the appended claims.

1. A projection type display apparatus, comprising: a light source foremitting a light; a first reflection portion, which is configured toreflect the light from said light source; an image display element,which is configured to modulate the light from said first reflectionportion; a lens group, which is made up with a plural number of lenselements, transmitting the light from said image display element; and asecond reflection portion, which is configured to reflect the light fromsaid lens group thereupon, wherein an optical axis of said light sourceis nearly perpendicular to an optical axis of said lens group, saidsecond reflection portion is so disposed that it inclines to an opticalaxis of said lens group at a predetermined angle, said light source isdisposed so as to bring an optical axis of the light source to be nearlyhorizontal, even if the projection type display apparatus is disposed ineither the nearly vertical disposition or the nearly horizontaldisposition.
 2. The projection type display apparatus, as described inthe claim 1, further comprising: a reversing potion, which is configuredto reverse an optical image when the projection type display apparatusis in the nearly vertical disposition, or in the nearly horizontaldisposition.
 3. The projection type display apparatus, as described inthe claim 2, further comprising: a gravity sensor, which is configuredto detect a disposition condition of the projection type displayapparatus by gravity.
 4. The projection type display apparatus, asdescribed in the claim 3, wherein said reversing portion exchanges saidoptical image upon basis of output of said gravity sensor.
 5. Theprojection type display apparatus, as described in the claim 1, whereinsaid lens group is constructed with a first lens group having arotationally symmetric surface configuration and a second lens groupincluding a lens having a rotationally asymmetric configuration on atleast one of the surfaces thereof.
 6. The projection type displayapparatus, as described in the claim 2, wherein said lens group isconstructed with a first lens group having a rotationally symmetricsurface configuration and a second lens group including a lens having arotationally asymmetric configuration on at least one of the surfacesthereof.
 7. The projection type display apparatus, as described in theclaim 3, wherein said lens group is constructed with a first lens grouphaving a rotationally symmetric surface configuration and a second lensgroup including a lens having a rotationally asymmetric configuration onat least one of the surfaces thereof.
 8. The projection type displayapparatus, as described in the claim 4, wherein said lens group isconstructed with a first lens group having a rotationally symmetricsurface configuration and a second lens group including a lens having arotationally asymmetric configuration on at least one of the surfacesthereof.
 9. The projection type display apparatus, as described in theclaim 1, wherein said lens group is disposed so that is inclines to anoptical axis of said image display element by a predetermined angle. 10.The projection type display apparatus, as described in the claim 2,wherein said lens group is disposed so that is inclines to an opticalaxis of said image display element by a predetermined angle.
 11. Theprojection type display apparatus, as described in the claim 3, whereinsaid lens group is disposed so that is inclines to an optical axis ofsaid image display element by a predetermined angle.
 12. The projectiontype display apparatus, as described in the claim 4, wherein said lensgroup is disposed so that is inclines to an optical axis of said imagedisplay element by a predetermined angle.
 13. The projection typedisplay apparatus, as described in the claim 5, wherein said lens groupis disposed so that is inclines to an optical axis of said image displayelement by a predetermined angle.